Think Out Loud

REBROADCAST: German scientist Peter Wohlleben on trees’ power to save us

By Sage Van Wing (OPB)
May 26, 2023 4:35 p.m.

Broadcast: Monday, Sept. 4

German scientist Peter Wohlleben captured global attention when he wrote “The Hidden Life of Trees.” Now, he’s followed up with a new book, “The Power of Trees: How Ancient Forests Can Save Us if We Let Them,” that essentially argues that we should leave forests alone, because trees are very good at adapting to whatever comes their way. We spoke to Wohlleben in front of an audience at Powell’s Books.


This transcript was created by a computer and edited by a volunteer.

Dave Miller: This is Think Out Loud on OPB. I’m Dave Miller. The German Forester Peter Wohlleben had written 15 books that didn’t make a huge splash before he catapulted himself into global attention with the “Secret Life of Trees.” It was essentially a translation of forest science for a lay audience and it became an international best seller. Wohlleben has followed that up with a new book. It’s called “The Power of Trees: How Ancient Forests Can Save Us if We Let Them.” In it, he argues that we should leave forests alone because trees are very good at adapting to whatever comes their way, even the profound effects of climate change.

We spoke to Wohlleben in front of an audience recently at Powell’s Books in downtown Portland; we started by talking about the ways that trees can learn. He has an example that involves trees in an ancient beech forest near where he lives. Some are on south facing slopes and others are on north facing ones. I asked him what these different sets of trees were used to experiencing?

Peter Wohlleben: On the southern slope, the beech trees have experienced drought because it’s more sunny, the soil is not as deep as on the northern slope. On the northern slope, they have had always enough water. They have never experienced a drought. There they have lived with rich water resources and they didn’t need to manage their water consumption on the northern slope.

Miller: So what happened when there were three successive years of drought?

Wohlleben: The beech trees on the southern slope, they looked well. On the northern slope for the first two years, they also looked well. Then in the third, very dry year, the drought reached the deeper soil layers. Then you saw that the beech trees were shot. I remember the first weeks of August in 2020, that they dropped off one third of their leaves within the day. That looked really bad and our son, gave him a phone call, and we went out and said, ok, perhaps they are gonna die, and no. The German forces just say that they were allowed in this year to cut down beech trees which dropped more than 30% of their leaves.

Afterwards, it turned out that they were just learning. Trees are able to learn very fast and that’s a normal reaction, to drop off leaves and then to wait, what will happen, and if the drought continues, they drop more leaves. Luckily, in this case, we had a big rain cloud going against our mountains. It stayed there for one day, leaving more than 60 liters per square meter. So they were good afterwards.

But for the next drought we had in 2022, you saw a different reaction because they didn’t drop leaves anymore because they have changed their way of water management.

Miller: What do you mean? So, two years after they had dealt with a potentially catastrophic drought, they sucked up water differently?

Wohlleben: Yeah. We have evidence that beech trees are changing their water management in years with more rain. Because they experience that there maybe a dry summer, so they make a break in summer time. They may produce a lot of sugar in May, in June, and then they make a break and then in autumn they continue. So all in all after, when the winter starts, they have enough sugar for the winter time. They stay healthy. They make a break whether it rains or not. So they change their behavior and what we know is that trees are able to give those knowledge to their offspring by epigenetic effects. The seedlings are much more climate resilient as the older trees.

Miller: Then there are some experiments that you write about that show this. How did they set up experiments to try to see what the offspring of trees - they got a lot of water or a little water - would learn?

Wohlleben: In Switzerland, [in] Zurich for example, they watered half a pine stand and the other half pine stand was dried out with roofs and for around about 10 years. Then they look [at] what the seedlings are doing during a drought. And the seedlings from this dried out pine stand. they were much more resilient to droughts than the seedlings from the old pines which were watered for 10 years.

So you see exactly that the offspring learned from the mother trees by epigenetic effects, but we don’t know if there are other effects. There may be also effects through the roots because they connect to the seedlings and perhaps even there, is a transfer of information.

Miller: How much can a beech tree change its behavior and can it change enough given the changing world?

Wohlleben: I think we should look at trees because trees are just a part of our ecosystem. And the whole ecosystem reacts and we always think, ‘Ah, the trees should be more climate resilient,’ or, if they aren’t, we should replace them by more climate resilient trees from southern-more species. That’s wrong, because we know that the whole system is reacting -- a tree knows since 300 million years that it’s not able to move if conditions change. So that’s the difference to us. A tree is able to change the condition back within a big ecosystem.

Alexander von Humboldt is a famous German researcher who was also in North America - a rock star of his time in science. He already knew that forests are able to cool down the local atmosphere around about 10 to 15 degrees on average in summertime. That’s 10 times more [than] what climate change actually does. They are able to cool down, they are able to create, actively, rain clouds. If it is too dry, they create rain clouds. How? They evaporate water. We think, no, but they consume water so that it’s even drier. No, the water isn’t the way, the water is above the trees. Then they evaporate certain substances and they evaporate billions of bacteria living on their leaves. The bacteria creates the clouds, more ice crystals and this falls down as rain.

So the intact forests, big forests, create water cycles. We as humans interrupt those water cycles by splitting the forest into small pieces, by cutting the old trees and old trees are like libraries. We know that trees, the longer they live, the more information they store. For example, in Germany there were the oldest oaks were researched. And in 1819, the droughts, they suffered very heavily. In the third year of the drought, they recovered and scientists researched the leaf shape and saw they changed the leaf shape to a Spanish oak type. That’s a different species. The explanation is that, these old oak trees perhaps remember their Spanish origin because the population of these oaks survived the ice age in Spain and came then back by birds of course. Now in this heavy droughts, they changed back to like they live in Spain and they recover and the seedlings get all this knowledge from the older trees.

Therefore, and it’s exactly here, the same in Oregon. It’s so important to keep the oldest trees. They are the most important ones. German forestry is exactly the same as it is here and it’s all about renewing the forest, making them more healthy but younger trees and that’s nonsense. The oldest trees are the most worthful, they contain the information. But besides that, the oldest 1% of trees contain 50% of the biomass of a forest. So it’s all about the oldest trees, not the youngest. The youngest, it’s easy to replace the trees themselves but old trees you can’t replace.

Miller: You went through a lot and I wanna unpack some of it. There is a lot to get to, but I want to go back to the trees that were the northern slope beech trees that were not used to drought, and one day they dropped 30% of their leaves. Why are they dropping their leaves to begin with? What is the specific reason for doing that?

Wohlleben: Yeah, it begins in the roots. The trees have brain-like structures. There are brain structures, brain-like processes going on even sometimes even with the same neurotransmitters - you can’t say neurotransmitters because plants don’t have neurons. So that’s the trick of science. It’s like in our brain, the roots notice it’s going to be drier than they produce hormones. It’s part of their body. We think a tree is a stem and the branches and the crown. But no, that’s a little bit like our stomach. The main tree is in the underground. We think, ‘Why do the trees drop the branches, the leaves?’ It’s because the roots realize it’s too dry and we have to close the little mouths on the back side of the leaves. If it is not enough, if there’s too much evaporation, they drop from the top down more and more leaves until the drought stops…

Miller: Because, otherwise they’ll lose even more water...

Wohlleben: …Even more water…

Miller: …Even more leaves mean losing water. It also means potentially making sugar and growing.

Wohlleben: No, no. They stop growing much longer before [that]. They stop, they reduce water consumption. If this is not enough, they stop for the tree’s sake completely. If this is not enough, they start to drop some leaves on the top and then, that’s a process. It’s like we are doing it when we feel uncomfortable, we try to make it a little bit more comfortable. If it is uncomfortable, you change more. So it’s a tree adapting until it’s ok.

Miller: But it’s also an emergency, right? I mean, by that point,

you, the tree can’t grow if it doesn’t have leaves, it can’t grow more at that point.

Wohlleben: Yeah. There are panic reactions, for example. With the horse chestnut, I describe in the book, there’s a row in the street where our Forest Academy is and this one horse chestnut obviously panicked and dropped all leaves off. When the cloud came that I described with a lot of rain, all other chestnuts started to make food and [inaudible] again. This one couldn’t because it hadn’t any leaf left. Then something strange happened. In October, when all other horse chestnuts were ready for winter sleep - Hibernation, like a bear. Yeah, this is exactly why they collect sugar. They don’t collect salmon, they collect sugar. This one horse chestnut realized ‘Oh, I don’t have enough sugar.’

Then it brought out new leaves which should be there for the next spring. It brought new leaves out and it flowered and the question is why? Many people think, ‘Ah, it’s, realized it’s gonna die so it tries to reproduce.’ No. Imagine if you’re hungry or thirsty and near starving to death, I don’t think the next thought will be, ‘I would like to have sex.’

[Crowd laughs]

No, if you’re if you need water or whatsoever but that’s not your last thought, hopefully.

Miller: No, I mean, that is how salmon do it.

Wohlleben: Yeah.

Miller: To be fair…

Wohlleben: Yeah, that’s another story I could tell. But to come back to the horse chestnut. As a tree you can just get pressure on your branches and then all buds come out. Whether flowers or blossoms or leaves. So it came out and it is of high risk because the days are shorter in October and November. We have the first frost days, frost with temperatures. I just know it in Celsius, below zero. So the question was, will it survive? Luckily it survived.

In the next spring, which is nearly impossible for horse chestnut, it didn’t flower. Because in autumn when it was very weak, it decided not to produce buds for blossoms. So you saw very clear on this little poor horse chestnut, the trees are able to make mistakes, the trees are able to panic. There was a heavy storm we suffered in Germany, it was 2022. This horse chestnut kept all its leaves on the branches. So this mistake wasn’t made again.

Miller: So let’s turn more deeply to the micro-climate-changing abilities of big stands of trees… of forests because you mentioned two things: atmospheric rivers making rain and also significantly cooling the air around them. How does the cooling work?

Wohlleben: Exactly as if we are sweating. Oh, wonder, we are getting cooler. This tree is evaporating around 500 liters of water per summer day. Imagine you were sweating 500 liters. That’s very cold.

Miller: So over 100 gallons of water.

Wohlleben: Yeah. This water, as I said, is the way, you can even feel it when you touch the stem. Beech trees, for example, have a very thin bark. They are cooler like oak trees in summer times because [of] the water from the ground pumping up into the crown. That’s the first step of cooling. The second is to evaporate the water. Then of course, the trees, the big forest, creates clouds above. That’s like an umbrella. So the sun is away and then it starts to rain, the net cooling effect. So all in all, you have 10 to 15 degrees temperature lowering.

Miller: Is that a beneficial byproduct, in a lot of ways, of photosynthesis and of the way trees exist? Or is it part of the plan after 300 million years of evolution?

Wohlleben: That is part of the plan. There’s a lot of things going on in the forest and as I said, we just regard trees. It’s the whole ecosystem which works together. For example, if you put two atoms together or three - two ‘H’ [Hydrogen] atoms and one ‘O’ [Oxygen] atom - it’s just gas. If you put them together, you have water or ice. So something really different is created.

If you put some bacteria together with other bacteria, that’s much more complicated, some crazy things are going on. So far, we haven’t detected more than around about 10% of all species living in a forest. For example, Norwegian Forest Scientists, they researched two spoonfuls of forest soil and discovered around about 40,000 different bacteria species, not 40,000 bacteria. Their were, I think, around about 50 billion bacteria in those two spoonfuls belonging to 40,000 different species. Just one species can make the difference.

We have, in the northern hemisphere, the Ash die-back from a fungi from I think Japan or so. Most of the Ashes are dying from this, but a certain percentage survive. We don’t know why until research was done last year. The scientists found out that one bacteria species, of 10 thousand, changed and mutated to a different chemical production and is now fighting against the fungi. Why? Because this little bacteria thinks, ‘My sugar donator is dying and then I’m dying too, so I should react.’ Now, I use the word ‘thinking’ - [you] may say, ‘Oh, that’s a little bit anthropomorphizing bacteria.’ No, it’s a single cell organism.

For example, slime molds, I think you can buy them as blop for children. It’s really nice to have it in your house. It’s moving. So you should be a little bit careful - no, very slowly moving. In Germany, also a podcast and it’s always good to talk to scientists about that. Just for example, from the University of Munich, there’s a scientist and she is researching the human brain. This singular cell organism, this slime mold which loves oat flakes, you can put it in a labyrinth. It finds the shortest way to its beloved oat flakes and is able to communicate to other slime molds it has a geographic mind - that means also memories and imagination of where it is… a singular cell organism. We just think, ‘Oh, it doesn’t have 1.5 kg protein on its neck. So it has to be stupid.’ That’s how we think it works. See this slime mold is regarded as a model how our brain works. Because it seems like the slime mold stores memory the same way we do. No, it’s the other way around. We store memories the same way slime molds do.

Miller: I think maybe that one of the biggest things that’s come up in almost every answer of yours so far is that as humans, and especially in certain realms of science, we are denigrating almost every or most non-human versions of life in various ways, right? Whether it’s trees or slime mold or bacteria. The underlying this, in your argument, is that this is one of the reasons that humans are living out of balance with the world. But can’t we change our ways without getting into a debate about what is intelligence? What is desire? What is emotion? What is anthropomorphizing?

I guess I’m wondering, in terms of your project of getting our species to change our ways in profound ways, why it is that you focus so much on questions of intelligence?

Wohlleben: Yeah, I think that’s how we see ourselves. We think we are something special - which we are - and slime mold is something special. A tree is something special. Trees don’t write books. They’re not interested in it, otherwise they would do it perhaps, I don’t know. But what we did since the Age of Enlightenment, that’s ages old. Since [the] stone age or so, that’s something relatively new that we see nature as something different. We are on one side that is anthropocentric, that we think nature serves us. It’s so important to see that we are still part of it.


I tell you a little thing and you see that you are still part of it. All of you are not individuals, you are not living on your own. You have, for example, the same amount of bacteria then you have body cells. The bacteria are communicating with you. They create your moods by producing hormones in your guts. It’s not the gut brain... that this bacteria that are communicating with you or this little guy is living in your face. Hair follicle mites are well adapted to our faces. They are 0.5 millimeters long. They don’t have eyes anymore. But they can see or realize that it’s night time by the melatonin level rising in you. Then they say, ‘Ah it’s night time, you are sleeping.’ Oh that’s perfect because then they come into your face and there they mate. So your face is their planet. Sorry for that. Every [one] of you has them. But why are we so, ‘Ewww…’ [and] a little bit shocked? Because we think ‘No, that’s me, and they don’t belong to me.’

No, we are part of this. We are an ecosystem. We are part of the ecosystem and to come back to your question, it’s very important to realize that sitting in this wonderful library is just possible because all those creatures around in the forest are working for us. This is a concentrate of human civilization, which is just possible because [there are] all these other beings around us that benefit us.

Miller: I want to take this back to a fascinating example that you write about that was brought to us from some Argentinian plant scientists and this gets to questions of cooperation among family members, among related plants. What did these Argentinian scientists do?

Wohlleben: Yeah, they did crazy things. They ask crazy questions. I love scientists asking crazy questions because otherwise we wouldn’t know very much. They ask if certain… I don’t know the word for this plant, it’s a little herb. It doesn’t matter what it is, perhaps. What I’m telling you may be found on other plants or perhaps on all plants, we don’t know because it’s just an example. This plant, they put in a laboratory and they ask if this plant could judge which other plants of the same species are family members. OK. That’s a strange question and to get money for this research should be very hard. But what you can observe is that they were planted in pots and then if they are family members, they keep their leaves away from each other. So every individual has enough sunlight. If they are not related, they grow into each other. So the food is not that optimal.

Miller: They compete for sunlight…

Wohlleben: They compete. The question is why? Then it’s hard science. You can judge this by genetic proofs, you can switch off some genes and one after the other and look if they behave different afterwards. As they switched off the gene which is responsible for seeing blue and red light, they didn’t realize that their family members were near them. So they have seen their family members. So that’s the first proof that plants [are] able to see if the neighboring plant is a member of its family.

So we say, ‘What? Plants can see?’ Yeah, plants can also hear. For example, they can hear the chewing sound of insects or plant-eating mammals and then they react. That’s a very new study, where the next question is, if we, with our human civilization sounds, are disturbing the defending reactions of plants because we are so loud.

Miller: Are there tree analogs to that plant experiment?

Wohlleben: There are tree analogs concerning some things. For example, trees are able to taste. They’re able to taste the saliva of deer. That was studied, I think, at the University of Leipzig. They pruned branches from little beech trees and then instantly started a wound healing reaction. If they dropped a little saliva of deer on the wound and then the tree started a defending reaction. So the tree knows what’s going on. The tree has a lot of senses to judge what’s going on. Roots, for example, can see light much better than we can. They’re much more sensitive [to] light. We’ve talked to scientists from the University of Bonn and she said they have made experiments bringing roots into a box which was very much light in and just a small black dot on a wall and the roots tried to flee to this dot because they hate light.

Miller: Huh. I was surprised . . . maybe I shouldn’t have been, but I was surprised to read in the new book that German foresters, for years now, have been planting Douglas firs in many parts of Germany. The state tree of Oregon, the tree on our flag, on our license plates. I mean, a hugely important native tree here. Why is it being planted in Germany?

Wohlleben: Yeah, because German foresters think the forest is not able to do it on its own. The highest ranking forest scientist, he is the head of an advisory team for the German government, says, ‘The nature is no longer able to heal itself and the forest is [no] longer able to work on itself because of climate change. Foresters have to save the forest by cutting trees and planting new ones.’ We say, ‘No, that’s the reason, that’s not of help.’

They say we should plant more climate-resilient trees which are adapted to hotter and drier climates. We say, ‘Just a moment, I think Douglas Fir… don’t like it very hot and very dry…’, don’t have to explain to you. But perhaps here should have been more German foresters, not like me, but the more traditional ones.

Some of my foresters are living in the forest house where we now live. [They] have planted Douglas fir trees and they are dying because of the heavy droughts we have in Germany. But although you can see this already, German foresters declare that Douglas fir or Red Oak from North America or Lebanon cedar will be a good choice Somebody said, for example, it’s conifer, which grows of course in Lebanon in heights of more than 1,000 meters and very much snow. This should replace dying spruce plantations that die because of heat. That sounds really crazy.

Miller [narrating]: That’s the German forester Peter Wohlleben, in conversation recently at Powell’s Books. At one point I asked him what challenges saplings face when they’re grown and planted in the ways that are most common in commercial settings these days.

Wohlleben: For example, if you buy trees from a tree nursery, in Germany, they would be called tree schools. Which is even more crazy because in such tree schools, the roots will be cut – brain extractions. It’s not good to cut them in school. And why? Because you can plant them much more [easily] or they are plant[ed] in little containers. Which is also a very hard life for trees, because if you plant garden plants in your garden for just one season and you put them off in autumn you see the pot shape and from the roots. So it’s not possible for trees to root correctly deep when the roots are cut off.

The next thing is the trees are perhaps from 500 kilometers away from someone who collects the seeds. I tell you a little experiment from Germany. In the Black Forest, there are mostly deciduous trees but some conifers like white fir. This white fir, they thought, ‘OK, if trees are able to adapt to climate change, it’s OK to have the same tree species from more southern populations, that will be OK,’ right? It’s exactly genetic from the same white fir. So they brought white fir from Southern Europe to the Black Forest and it didn’t grow. Why? So they made molecular genetic research. It’s really hard science. They found out that the fungi didn’t accept southern-more white fir. When we say, ‘Just a moment, that’s 100% white fir…’ and the fungi says, ‘No, it isn’t;’ the fungi is always right. Yeah. It’s a human category to say that’s white fir. It’s just 1,000 kilometer more in the south. The fungi said, ‘I said, no,’ it’s a different species. I don’t accept it.’

Miller: Well, that gets to something . . . We’ve had a number of conversations on Think Out Loud over the last couple of years with, I think very well meaning forest scientists, people who are not out to chop down as many trees as possible, but to save particular species. [People] who earnestly say that, in some cases, it makes sense to save trees that cannot adapt fast enough. Despite everything you’ve said, it makes sense to find some that are not gonna survive where they are and put them 200 miles north. You’re saying this has been done and it doesn’t work. They say if we don’t do it, we might lose some of these trees forever.

Wohlleben: If these were the last trees on earth, I would try this too. But I think that that isn’t the case. The thing is we have to understand that it’s all about an ecosystem. It’s not about special species. Forest ecosystem contains, I think more than hundreds of thousands of species and the little ones, like the [inaudible], are exactly as important as big trees. But we’re always in ‘my big things. Oh, that’s tall. Ok.’ That’s crazy. ‘The little ones ‘ah that’s not so important.’ But the tree is a mixture of thousands of species. So, as long as you don’t know exactly, you have to respect that it’s better on its own.

It’s like you want to save endangered animal species just living in zoos without the natural habitat. That’s a very sad thing. That would be the very last solution. Then it’s ok. But first, we should bring all our power into make forests more resilient. That means that trees grow old. That you have big forests like you luckily have here. In Germany, they are very fragmented. We have our forest planted in around two million pieces, very small forest. If they cool down the local atmosphere and they are very small, warm air comes in. So it’s all useless. So it’s all about big forest, old trees, and a lot of deadwood. I know that’s a big topic here. But what we are talking about are not dead wood on clear cuts. It’s dead wood with thick trunks and thick stems which are like sponges, soaked full of water, and that are fire breaks. They don’t fuel fire.

Miller: I’m glad you brought up fire. Which is, I think this is true, a much bigger deal in the American West right now than it is in Germany. Although it’s possible that too could change. As I’m sure you know, for thousands of years, Indigenous people in the West used fire as a human tool on the landscape. Then for about 100 years, the Euro-American policy has been the exact opposite – not only not prescribed burns, which we call now, but putting out basically any fire so it couldn’t become a small one.

If your biggest, overall prescription in terms of what humans should do is ‘don’t do anything’ then how do you approach the question of prescribed burns after a century of fire suppression?

Wohlleben: A century is nothing. If we go back, let’s say 10 million years, without any human influence these forests managed to survive otherwise they wouldn’t be there now. So they are able to do this on their own.

Miller: When you say ‘this,’ what do you mean?

Wohlleben: Yeah, forests are adapted to all those things. The trees like to have stable conditions. So they do everything to avoid big fires. Ground fire, not very hot, let’s say 300 or 400 degrees, that’s ok for trees. The ground fire with 700 degrees celsius, burning the complete tree, that’s not ok. That’s exactly what we see now. Why do we see this? Because most of the forests have been managed heavily. Where the old trees are gone, in most cases. If we have some little spaces left and we have big wildfires in human managed forests, then also these little islands of old growth forest will be destroyed.

We see it in Germany, it is exactly the same. We have never had wildfires in German forests until German forestry has started to manage and replace species and make even-aged tree stands. What you also have here, in most cases, are young forests where the bark of the tree is not as thick as it should be. Where the deadwood amounts are not very big and so on. So we see young forests, many forests and if you leave this forest on its own yeah the data of fire is, for some decades or perhaps one or two centuries, higher. But in the long term, I’m convinced it’s lower because trees are not interested in being burned.

Miller: I just wanna make sure I understand what you’re saying because the argument of both Native tribes and increasingly, the broad forest management community, is that because we’ve put out every possible fire now there’s a possibility for catastrophic fires. So because of that, we should both let some fires burn when lightning strikes or when power lines aren’t turned off. In addition, we should have small, carefully managed fires here and there to make it more like the way it used to be before. In other words, it’s humans doing things because humans for 100 years did too much. Even that, you’re saying, is still too much human work?

Wohlleben: Yeah. If it comes to Native tribes, for example, they managed forests with old trees. That’s a different thing, to light the ground fire in an old forest. But now we think, ‘Ok, they [lit] fires in old forest, so we [to] light fire in young forest.’ No, that’s something different. Young forest, they have to concentrate biomass.

Where do the wildfires start? In many, many cases on clear cuts. On clear cuts, the soil dries out. You have high temperatures that you can boil eggs. So it’s dry and most fires, I’m heavily convinced, are human caused. We say, ‘Oh, it’s lightning, that’s by nature.’ No, it’s as you say, power lines, cigarettes, by purpose, whatever. In Germany, we have the same discussion. No, timber just didn’t burn because the sun is shining. So it’s the big clear cuts. The first thing if you want to avoid wildfires, you have to stop clear cuts. As long as you make clear cuts and say, ‘Oh, we have wildfires, so we have to burn even the forest where the trees are intact.’ That is a crazy method to make the forest more resilient.

So first stop clear cuts, let trees grow older, perhaps in between in some regions surrounding. For example, the villages that’s something different to protect people, that’s always ok to do. But in other cases, the biggest problem, to be honest for the forest, it’s not the fire. It’s the heavy use of timber. We should reduce this. We should make just a light thing of forests. We should forbid clear cuts as long as you are interested [in having] less fire.

Miller: This gets to one of your other prescriptions, which is that a carbon tax should be extended to all wood that’s chopped down, to all wood products. Whether it’s for paper or building homes or toilet paper or whatever. What’s your reasoning?

Wohlleben: The reason is…that’s widely accepted by science, except forest science. If I have to say this – forest science, its origin is in Germany. In Germany, a special situation [is] that the German forestry admission is the biggest timber seller. Although it should be control the law. So it controls itself. So it says ‘Everything is fine, to thin the forest is to make it more resilient because less timber can be burned in wildfires. Ok?’ It’s the same narrative that you have here. It’s carbon neutral because when you cut a tree and you will grow and will take up exactly this carbon. I always wonder, how will the tree differ which carbon comes from coal and from trees?

So, it’s widely accepted among scientists that burning timber is worse than burning coal. Just concerning the carbon effect, if you consider the cooling effect of the atmosphere, if you consider the water cycle... For example, you are depending on the Amazon forest. I don’t know if you know this, with your rain here, and we say, ‘Oh, it’s El Nino.’ No, it’s Amazon forest. So if you put all this together, it’s the worst thing to burn timber. Not for a little fire for your evening and summer time or so but to burn it in power plants. For example, in the US, there are big, big clear cuts in the Southeast for European power plants. Because of the big influence of the forest industry, Europe regards timber burning as carbon neutral – and that’s environmental crime. We should stop that. If we stop that, we have enough timber for houses, for books, for whatever. Because the biggest amount of timber use is for burning, for energy production.

How will you control how much is enough? You can measure the temperature of a forest if it gets fever by satellite. We have all those lovely instruments. Nowadays, you can see if the forest gets warmer after the thinning, then it was too much and then you have to stop it for years until the forest recovers. So we can measure this. It’s exactly like you. If you got fever, you don’t know exactly what your blood is doing and your killer cells or whatsoever. It’s enough that you know, in celsius it’s 42 degrees, and after that you have to stop it. That’s exactly what we see [in the] forest. If the temperature rises too high, you have to stop it. So you can control it very effectively. You can control the biomass amount. We have all those instruments, which are not in use in forestry. There are more and more web pages where you can control by yourself what’s going on in the front of your door, in your forest, and the forest industry hates those instruments because you can control them now.

The app should be better, like bird apps or webs on herbs or whatsoever. We should get, and I think we will have one within the next years, where you are able to control all those parameters very easily. No, you don’t have to be a scientist. You can just see, ah, that’s our forest. Oh, it’s looking bad. Oh, that temperature and what about the biomass? It’s gone. Ok. So no one can tell you anything anymore.

Miller: It seems to me that one of the challenges we face as a species when trying to wrap our heads around trees, is the difference in time scale of our lives and the potential lives of trees. In recent centuries, we haven’t let them get as old as they could. But this gets to a version of human impatience. How do you think about time?

Wohlleben: Yeah. I tell you an example. I’ve got a friend, an old forester, who advises some companies in Chile, for example. He was there and they talked about a set up which didn’t reproduce for centuries and they thought that it will be extinct one day. One of the guys said, ‘Ok, I fly you in the mountains and then I show you something’ and he showed them many young setups on a mountain, where part of the mountain came down. These are the special conditions this tree needs. And if there is, let’s say for 500 years, not such an event, you won’t see young trees of this species.

So, it’s our thinking in forest terms. We have been educated in Germany and because of German foresters who were also here 100 years ago, you can go wherever you want. German foresters were there in India and New Zealand and Australia, in wheresoever,...

Miller: [Interjecting] … and spreading the gospel of trees as a farm.

Wohlleben: Yeah. The narrative is forests have to be renewed with young trees and if you don’t have young trees, something goes wrong. No. Trees can become old. Some effects appear. For example, there are lichens which just grow on spruce trees older than 500 years. So some processes take time and if you don’t have young trees on a certain spot for 100 years, it’s OK.

Miller: But how do you help those of us who have a hard time thinking about a 500 year time scale? How do you switch our brains to slow down in that way? I guess what I’m saying is that I’m not gonna be around in 500 years. So I’m not going to see that. I may see nothing of the longest term benefits of what you’re talking about. I’m never gonna see that. So how do you sell those of us who are just not used to thinking about time in that way?

Wohlleben: First thing is if you want to see a recovering process, that starts very fast and it’s slowing down from year to year, more and more. So an old forest, you almost see no difference if you would be away for 10 years and come back. You see it’s all looking the same. If you see cultivated land like farmland and you let it on its own, then it recovers very fast. So it’s in our time scale.

Like Chernobyl, for example, where the nuclear catastrophe happens in 1986. It was fenced in because of the risk with the nuclear things and around 400 square kilometers, it’s like a national park and now the wildland is returned and it’s completely wild with forest, with peatland, with a lot of wild animals - which are resilient to toxic things. Meanwhile, 36 years and it’s completely recovered. So that’s going very fast.

Trees are fast in healing wounds as long as we let them. But when we listen to forest scientists, like the one I told you, we think, ‘Ah, forests are so weak, and we have to help them. We have to plant.’ Planting is a good thing – I don’t want that you misunderstand me – in cities you can do so or where no forest is within a range of, let’s say 10 miles or so. Then it’s ok to plant on farmland. But in all other land, trees come back. It’s one of my hobbies to look in train stations, I think the day after tomorrow, I will do it here. For example, in Hamburg track 14, there’s a little cherry tree in Cologne. Track 11, where it’s the main track, where all those rapid trains are going over, there’s a little Acer tree, four years old. Also, this track is sprayed with Round-up and it’s very hot in summer time and very dry. So the trees are able to learn and they can stand very rough conditions. So we don’t have to help them. We have to let them on their own.

Miller: You’ve become internationally famous for translating tree science to the general public and in a sense, explaining some things that maybe in the past have been mysteries to us. What is still one of the biggest mysteries to you about trees?

Wohlleben: Perhaps, I tell you a little story about our daughter. She said, 20 years ago, while sitting at the breakfast table, that, ‘It’s very strange that we always try to train animals to speak our language.’ Yeah, like parrots or chimpanzees or whatsoever. ‘It would be much more intelligent if we learn their language.’ If we are most intelligent, we should be able to. If a parrot can learn human language, you should go the other direction. But I don’t know anyone who speaks chimpanzee, for example. To answer your question, it wouldn’t be my greatest wish to speak tree. Although I try. To listen to them, for example, that could be done by a computer because trees are communicating by smell, by electrical signals. There should be a decoder someday where it can translate. They just say, ‘Ugh, leave me alone.’


Miller: Thank you very much for your time. I really appreciate it.

Wohlleben: Thank you.

Miller: That’s the German forester and author, Peter Wohlleben. His new book is called “The Power of Trees: How Ancient Forests Can Save Us if We Let Them.” We talked earlier this month in front of an audience at Powell’s Books.

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